| Soil erosion has seriously affected regional grain production and environmental quality in the southern Ningxia Loess hilly region.Ecological restoration and construction projects,such as “Grain for Green” Program and small watershed management,has been pursued in this region to prevent soil erosion and environmental degradation.However,there are still intractable ecological problems caused by gully erosion.Therefore,there is a need to study the effect of gully microtopography on vegetation and soil properties,as well as soil-vegetation correlations.With the text,this study analyzed the effect of different parts of the erosion gully(gully head,gully bed,and gully bank)on vegetation characteristics,soil physicochemical properties,and soil erodibility factor K in Yuwa watershed of Pengyang County in the city of Guyuan in Ningxia Hui Autonomous Region.The main results are as follows:(1)The gully head plants belong to 3 families and 6 genera,Gramineae include 4genera and 4 species,Umbelliferae include 1 genus and 1 species,Leguminosae include 1genus and 1 species.The gully bed plants belong to 5 families and 12 genera,Gramineae include 4 genera and 4 species,Compositae include 5 genera and 5 species,Leguminosae,Rubiaceae and Umbelliferae respective include 1 genus and 1 species.The gully bank plants belong to 3 families and 7 genera,Gramineae include 4 genera and 4 species,Leguminosae include 2 genera and 2 species,Umbelliferae include 1 genus and 1 species.In terms of life style,all parts are dominated by perennial herbs with annual and biennial herbs.Aboveground biomass,species richness,Shannon-Wiener index,and Margalef index showed gully bed > gully bank > gully head,Simpson index showed gully head > gully bed > gully bank,Pielou index showed gully head > gully bank > gully bed.Fine root biomass of each part of the erosion gully decreased with the increased of soil depth.Fine root biomass,specific root length,and root length density showed gully bed > gully bank > gully head.Diameter of fine root showed gully bed > gully head > gully bank.(2)Soil bulk density of each part of the erosion gully first increased and then decreased with the increased of soil depth.Soil bulk density showed gully head > gully bank > gully bed.The total porosity of the soil at the gully head and gully bank were both less than 50%.On the contrary,the gully bed improved soil permeability and water holding capacity.Soil water content and total porosity showed gully bed > gully bank > gully head.The mechanical composition of soil in each part showed silt content > sand content > clay content.Soil organic carbon,total nitrogen,and total phosphorus contents showed gully bed > gully bank > gully head.The main particle size of soil non water-stable aggregates in various parts is >5 mm,while the main particle size of soil water-stable aggregates is < 0.25 mm.Water-stable aggregates,weight diameter of soil,and geometric average diameter of soil showed gully bed > gully bank > gully head;Soil erodibility K value showed gully head > gully bank > gully bed.(3)There were significant correlations among vegetation characteristics,soil physicochemical properties,and soil erodibility factor K in each part of the erosion gully.Soil mass water content in gully head was positively correlated with aboveground biomass and fine root biomass.Soil mass water content was positively correlated with mean diameter of fine roots,biomass of fine roots and density of root length.There was a significant positive correlation between soil mass water content and aboveground biomass,fine root biomass and root length density.The total porosity of soil in gully head and gully bed had a significant positive correlation with Patrick richness,the total porosity of soil in gully head had a significant positive correlation with Shannon index,and the total porosity of soil in gully bed had a significant positive correlation with Simpson dominance.The content of soil organic matter was positively correlated with the biomass of fine roots,the mean diameter of fine roots and the density of root length.There was a significant positive correlation between soil organic matter content and aboveground biomass at gully head and gully bank.There was a significant positive correlation between soil organic matter content and Shannon index.There was a significant positive correlation between soil total P content and aboveground biomass in gully head and gully bank.The content of water stable aggregates > 0.25 mm,the mean weight diameter of soil and the mean geometric diameter of soil were significantly positively correlated with the biomass of fine roots and the density of root length.The content of water stable aggregates > 0.25 mm was positively correlated with Shannon index.Soil erodibility K was negatively correlated with aboveground biomass and fine root biomass of plants at each part of erosion gully.Soil erodibility K was positively correlated with soil organic matter and soil sand content,and negatively correlated with soil total nitrogen.Soil erodibility of gully bed was significantly negatively correlated with the content of > 0.25 mm water-stable aggregates,the average weight diameter of soil,the average geometric straightness of soil,and the soil clay content,and significantly negatively correlated with the content of soil silt and positively correlated with the content of soil sand.The soil erodibility of gully bank had a significant negative correlation with soil clay content,a very significant negative correlation with soil silt content and a very significant positive correlation with soil sand content.In general,the higher the content of clay particles and silt particles in the soil of gully head,gully bed and gully bank,the more soil water-stable aggregates,the better the stability,and the stronger the soil resistance to erosion.In summary,plants in gully bed has a more developed root system than that in the gully head and gully bank,which improved competitiveness and growth rate.It was profit for plants to take up adequate water and nutrients,which promoted plant growth and hence enhanced soil erosion resistance.However,there were strong water erosion and gravity erosion in gully head,which had significant impact on plant growth and organic matter accumulation.This may decrease the quantity and stability soil-water stable aggregates and hence decreased soil erosion resistance.The gully head is prone to collapse and the soil moisture condition is poor in gully head.Therefore,there is a need to deploy native tree species in gully head with developed roots,strong stems,strong scour resistance and drought tolerance.Herbs or shrubs with high water demand can be preferentially deployed in gully bed and gully bank. |
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